1. Field of the Invention
This invention relates to deformable mirror systems, and more specifically to active segmented mirrors for use in the laser field.
2. Description of the Prior Art
In accordance with the present invention there is provided an active segmented mirror which has a plurality of performance and fabrication advantage over the prior art. First, operating bandwidths are not affected by mirror surface heat exchanger stresses or restraints. Low elastic stresses are maintained in all components even with extreme heat loads and operating frequencies and deflections. Operating bandwidth and life are basically restricted only by actuator capability offering ready growth to futuristic requirements with minimum design change. Mechanical resonances are characteristically several kHz, making high frequency, large amplitude operation practical.
Mirror size is relatively independent of heat exchanger induced distortion providing extension to very large mirrors with minimum design and fabrication impact. Larger or smaller mirrors may be obtained by changing the supporting structure and manifolding. Scaling of elements from 1/2.times. to 2.times. also appears practical, providing a range of corrector precision to satisfy system performance and control requirements.
The elements in the proposed mirror can be polished in groups mounted in a rigid support structure. The ability to polish flat mirrors while maintaining figures to within 0.002 inch of the edge has been demonstrated. The individual segments are coated after polishing. The total mirror is assembled after the surface finishing operations. Assembly tolerances are relaxed by the ability to adjust and trim segments mechanically during assembly. This trimming feature may also be used to make static optical figure changes.
Figure stability is improved since thermal expansion of heat exchanger elements does not affect the overall structure. The inherent rigidity of the mirror components also aids stability when subjected to acoustic, vibration, and maneuvering loads. Since large forces are available in the actuators, the segment suspension sections may be designed to be quite rigid when viewed by environmental disturbances, yet sufficiently compliant to permit wide band operation.
Control is simplified, as motion of a segment is not influenced by loads transmitted or induced by adjacent sections of the mirror. The surface is also free of complex resonance variations arising from physical structure changes caused by deflection of adjacent sections.
Reliability is improved by the simplicity and independence of the proposed segment configuration. Each segment may be tested and inspected independently before assembly. Should failure occur, its effect is minimized and repair is readily accomplished by segment replacement. By employing proper techniques, an actuator or mirror segment or both may be replaced without disturbing the remaining assembly.
Alignment and trimming of individual sections of the mirror is simplified since adjustment of one segment does not affect position of adjacent sections as occurs when loads are transmitted through common compliant structure.
Thermal management of actuator components as required to ensure stability is simplified by their isolated position behind energy absorbing structure. The actuators are cooled by conduction both into the strut and support structure.
The small size and accessibility of the individual segments permits a great deal of latitude in heat exchanger design. Since gross mirror distortion caused by thermally induced bending is basically a function of the diameter of the mirror squared, the small size of the segment permits relatively simple coolant circuits to be used as compared with larger mirrors. The small segments are also more readily adapted to advanced fabrication techniques.